The present invention relates to a novel bracing system for use in building structures.
Building structures employing vertical framing members, such as metal or wooden studs, have been strengthened to resist shear or lateral forces created by wind forces and/or seismic loading. In the past, such strengthening measures have taken the form of plywood shear walls fastened to the wooden or steel studs, held thereto by fasteners such as nails, staples bolts and the like. In addition, anchor bolts and hold downs have been employed to securely faster the frame structure to a foundation, such as a pier and grade beam foundation, a spread footing foundation a slab foundation, and the like.
Experience in actual earthquakes have shown that the combination of shear walls, composed of plywood, and nails are not sufficient to prevent damage to structures in this situation. It is believed that the estimated yield strength of nails normally used to transfer horizontal forces to a sill, ignores rotational forces. As a result, the stresses on nails in a typical shear wall may be as much as three to four times higher than their yield strength in a seismic event. It has been found that the ignoring of the vertical components from overturning moments in a frame shear wall has resulted in major structural failures during earthquakes.
Prior structures have been devised to reinforce buildings. For example, U.S. Pat. Nos. 4,875,314 and 5,448,861 show anchors which tie into the foundation of a building and extend upwardly therefrom through the use of tie rods.
U.S. Pat. No. 5,531,054 discloses a reinforced wooden wall in which foundation linked tie rods extend through the entire story of a building.
U.S. Pat. No. 5,664,389 shows a strengthening method against earthquake shock in which foundation reinforcing bars are linked to ceiling joists by special clamps.
U.S. Pat. No. 5,337,535 discloses a panel system in which the panels lock in side-by-side configuration to form wall ceilings and roof sections.
U.S. Pat. No. 4,251,965 describes a modular wall section which employs plates that extend between studs. The plates possess flanges that permit the plate to be fastened to the studs above the sill of the building.
A shear wall lateral bracing system which eliminates the need for foundation mounted tie downs and shear wall panels would be a notable advance in the building industry.